Clipping indicator circuit for transistor amplifier

Abstract

A light-indicator circuit is disclosed which permits visual indication of clipping caused by the over-driving of a transistor amplifier. The circuit includes a light-emitting diode connected in parallel with the collector-emitter path of a switching transistor which is biased to conduct during low-signal-level operation of the amplifier. The switching transistor is caused to switch to its non-conducting state when the amplifier is overdriven, thereby activating the light-emitting diode. Means may be provided to delay switch-back once activation of the light-emitting diode has occurred. Means may be provided to inhibit activation of the circuit by over-driving signals of limited duration.

What I claim is: 
     
       1. A clipping indicator circuit for use in conjunction with a transistor amplifier, said amplifier being comprised of an amplifying transistor with a collector-emitter path, a load electrically connected in series with said collector-emitter path, at least a first and second source of d-c potential between which sources said series connected load and collector-emitter path are electrically connected such that said collector-emitter path forwardly conducts from first to second potential source, and a bias and input signal means coupled to said sources and to the base of said transistor, said circuit further comprising: a switching transistor with a collector-emitter path and a base-emitter path;   a light-emitting diode electrically connected in parallel with the collector-emitter path of said switching transistor and having forward conducting path directed parallel to the forward conduction of said collector-emitter path of said switching transistor;   a current-limiting resistor electrically connected between said first source of electrical potential and the collector of said switching transistor;   a level-determining means electrically connected between said second source of electrical potential and the emitter of said switching transistor;   a bias resistor electrically connected between said second source of electrical potential and the base of said switching transistor; and   a sensing diode electrically connected between said base of said switching transistor and a junction in said series connection between said load and said collector-emitter path of said amplifying transistor.   
     
     
       2. The clipping indicator circuit of claim 1 in which a capacitor is electrically connected between said base of said switching transistor and one of said sources of direct-current potential. 
     
     
       3. The clipping indicator circuit of claim 2 in which a delay resistor is electrically connected in series with said sensing diode. 
     
     
       4. The clipping indicator circuit of claim 1 in which said level-determining means is comprised of a resistor. 
     
     
       5. The clipping indicator circuit of claim 1 in which said level-determining means is comprised of a zener diode. 
     
     
       6. The clipping indicator circuit of claim 1 in which said switching transistor is further comprised of a Darlington-connected pair of transistors. 
     
     
       7. The clipping indicator circuit of claim 1 used in conjunction with said transistor amplifier, said transistor circuit further comprised of a feedback-bias means electrically connected between said amplifying transistor and said first source.